1. Field of the Invention
The present invention relates to a test stand for a cylinder head of an internal combustion engine or for any part located in its immediate environment, such as a cylinder head gasket, fastening screw, etc., said engine comprising at least one combustion or pressure chamber. More particularly, it relates to such a stand for cylinder head components comprising at least means for supplying a hydraulic fluid to the combustion or pressure chamber, and means for controlling the pressure of this fluid so as to simulate pressure cycles in the combustion or pressure chamber.
These test stands are designed to accommodate either an engine cylinder head alone or a cylinder head mounted on its engine block. Pressurized hydraulic fluid is introduced into the combustion or pressure chambers, while a heat-transfer fluid is made to flow in the cooling pipes of the cylinder head with or without a block in order to keep it at a predetermined operating temperature. The means for controlling the pressure of the hydraulic fluid are designed to vary this pressure cyclically so as to simulate the operating cycles of the engine.
The operating conditions of the engine both with regard to the temperature in one or more water chambers and to the pressure in the combustion or pressure chamber are therefore reproduced by means of such a test stand. It is thus possible to study its behavior under thermal and mechanical stresses and its fatigue resistance, and consequently to optimize its design with regard to its layout and to the alloys used, the molding and machining methods or the heat treatments carried out.
Furthermore, such test stands may be used to study the behavior of some parts in the immediate environment of the cylinder head, such as the cylinder head gasket, fastening screws, etc.
2. Description of Related Art
A test stand of the type summarized above is known through document EP-A-0 415 857.
In that document, the means for controlling the pressure of the hydraulic fluid in the combustion or pressure chambers consist of injection pumps, the pistons of which are set in motion by cams rotated by an electric motor. The profile of a pressure cycle is therefore mainly determined by the shape of the cams.
In general, such a device is satisfactory. It is however relatively limited because the pressure cycles are produced in a purely mechanical manner.
In the first place, the duration of each cycle cannot be reduced as much as would be desirable in order to simulate engine speeds which are constantly tending to increase.
The design of current test stands also has limitations with regard to the maximum pressure to be reached. Now the maximum pressures in the combustion chambers are tending to increase for diesel engines.
Finally, the profile of the operating cycle is fixed by the shape of the cams. Therefore it cannot be adjusted with great accuracy, or easily modified.
Furthermore, maintenance of the stand is relatively expensive since it requires changing the camshaft, generally after several hundred hours of operation. This is because the cams wear rapidly with time, and their profile changes, thus impairing the regularity of the operating cycles.
The present invention aims to alleviate these drawbacks.
More specifically, the aim of the invention is to provide a stand for testing fatigue in cylinder heads alone or in cylinder heads mounted on an engine block, which makes it possible to reproduce more faithfully the pressure cycles on a cylinder head of an internal combustion engine at the operating temperature of the cooling circuit.
The aim of the invention is also to provide such a test stand which can reach higher operating frequencies and pressures.
The aim of the invention is also to provide such a test stand, the maintenance of which is easier and less expensive than that of existing test stands.